nir/ntt: Set a variable as invariant also if it is declared precise and pass invariant flag to TGSI

The "precise" keyword results in more strict limitations on the possible optimizations that can be applied to obtain the value declared with it then the "invariant" keyword, hence a variable that is declared precise also fulfills the requirements for being invariant, consequently set the invariant flag on a variable that was declared precise.

Pass the flag to the IO sematics and to ntt. Fixes dEQP-GLES31.functional.primitive_bounding_box.triangles.tessellation_set_per_primitive.vertex_tessellation_fragment.fbo in virgl when NTT is used.